In a communication network, network components are connected via communication links and usually share network resources. An important one of such network resources is for example the bandwidth used for communication between two network components. Due to limited availability of communication bandwidth, communication networks need means and functionality for managing the allocation of the available bandwidth for the different communication links between network components.
For example, sophisticated functions and measures pertaining to Quality of Service (QoS) in telecommunication networks for signalling and managing resource demands are necessary in order to build complex service-oriented packet-switched networks using the widespread IP protocol. Some approaches like Diff-Serv (RFC2475, compare S. Blake et al., An Architecture for Differentiated Services, Request for Comments, IETF, December 1998) rely on logically connectionless network services. However, more sophisticated and reliable services like IntServ (RFC2205, compare R. Braden et al., Resource ReSerVation Protocol (RSVP)—Version 1 Functional Specification, Request for Comments, IETF, September 1997), MPLS (RFC3031, compare E. Rosen et al., Multiprotocol Label Switching Architecture, Request for Comments, IETF, January 2001), and some kinds of VPNs (Virtual Private Networks), rely on connection-oriented semantics. Herein, a connection simply refers to a virtual abstraction of an ordered data flow, regardless of how that data flow is established or managed.
Especially in conjunction with very high demands of network resources, connection-oriented semantics can be essential for a thrifty resource management within a QoS-aware network. Since distributed applications are used by a variety of entities, including humans, it is often necessary to assure that network resources can be made available to a distributed application at a predefined point in time. For that purpose, some proposals for advance reservations are in place.
Advance reservation means a reservation of a network resource or of network resources in advance. It ensures that network management entities can properly schedule their available network resources and assure that network resources requested my means of advance reservation can be guaranteed for the scheduled time slot. In conjunction with an RSVP signalling protocol (RSVP—Resource reSerVation Protocol), such advance reservation mechanisms have been described in L. C. Wolf et al., Issues of Reserving Resources in Advance, Lecture Notes in Computer Science, 1995, and D. Ferrari, A. Gupta, G. Ventre, Distributed Advance Reservation of Real-time Connections, in Proceedings of “Network and Operating System Support for Digital Audio and Video”, 1995. The fundamental difference between advance reservation (also called scheduled reservation) and “normal”, so-called ad-hoc reservation is that for the advance reservation, the desired start time as well as the duration of the reservation are known or must be given. In contrast, no start time or duration needs to be supplied for an ad-hoc reservation.
Since an ad-hoc reservation corresponds to semantics of almost conventional connection-oriented applications, the coexistence of ad-hoc reservations with advance reservations must be ensured. This constraint leads usually to partitioning of network resources and therefore to less efficient network resource usage. Alternatively, the partitioning can be avoided, but this would lead to an inefficient resource scheduling. To reduce the drawbacks of resource partitioning, some measures have been proposed to make the partition border dynamically movable to some extent.
Nevertheless, performance-oriented or “performance-greedy” applications, such as applications within film production environments, often demand use for all or nearly all of the available network resources, leading to failure of the above described partition schemes.